U.S. patent application number 15/290645 was filed with the patent office on 2018-04-12 for low volatility, high efficiency gas barrier coating for cryo-compressed hydrogen tanks.
The applicant listed for this patent is PALO ALTO RESEARCH CENTER INCORPORATED. Invention is credited to GABRIEL IFTIME, DAVID MATHEW JOHNSON, QUENTIN VAN OVERMEERE.
Application Number | 20180100047 15/290645 |
Document ID | / |
Family ID | 61829896 |
Filed Date | 2018-04-12 |
United States Patent
Application |
20180100047 |
Kind Code |
A1 |
IFTIME; GABRIEL ; et
al. |
April 12, 2018 |
LOW VOLATILITY, HIGH EFFICIENCY GAS BARRIER COATING FOR
CRYO-COMPRESSED HYDROGEN TANKS
Abstract
A bilayer object consisting of a carbon fiber reinforced polymer
substrate coated with a composition of matter comprising
horizontally aligned exfoliated graphene sheets dispersed in an
epoxy binder. A method includes depositing graphene into a
hardener, mixing the hardener and the graphene to produce a
homogenous composite mixture, adding a resin material to the
composite mixture to produce an epoxy graphene material, coating a
structure with the epoxy graphene material, aligning the graphene
sheets in the in-plane orientation, and curing the epoxy graphene
material.
Inventors: |
IFTIME; GABRIEL; (DUBLIN,
CA) ; VAN OVERMEERE; QUENTIN; (MOUNTAIN VIEW, CA)
; JOHNSON; DAVID MATHEW; (SAN FRANCISCO, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PALO ALTO RESEARCH CENTER INCORPORATED |
PALO ALTO |
CA |
US |
|
|
Family ID: |
61829896 |
Appl. No.: |
15/290645 |
Filed: |
October 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 3/042 20170501;
F17C 2260/036 20130101; F17C 2203/0604 20130101; B05C 5/0254
20130101; C08J 7/0427 20200101; F17C 2203/0607 20130101; F17C
2203/0673 20130101; C01B 7/0743 20130101; F17C 2203/0619 20130101;
F17C 2221/014 20130101; B05D 1/265 20130101; F17C 2221/012
20130101; F17C 2203/0646 20130101; F17C 1/12 20130101; F17C
2221/013 20130101; C08K 3/04 20130101; B05D 3/007 20130101; F17C
2203/0643 20130101; F17C 2203/032 20130101; F17C 2221/011 20130101;
F17C 2270/0168 20130101; F17C 2203/0391 20130101; C01B 3/00
20130101; F17C 2223/0161 20130101; C08J 2463/00 20130101; C08J
2300/00 20130101; F17C 2221/015 20130101; F17C 1/00 20130101; F17C
2221/033 20130101; Y02E 60/32 20130101; F17C 2203/0663
20130101 |
International
Class: |
C08J 7/04 20060101
C08J007/04; C01B 3/00 20060101 C01B003/00; C08K 3/04 20060101
C08K003/04; B05D 3/00 20060101 B05D003/00; B05D 1/26 20060101
B05D001/26; B05C 5/02 20060101 B05C005/02; F17C 1/12 20060101
F17C001/12 |
Claims
1. A bilayer object consisting of a carbon fiber reinforced polymer
substrate coated with a composition of matter comprising
horizontally aligned exfoliated graphene sheets dispersed in an
epoxy binder.
2. The object of claim 1 wherein the coating consists of chemically
bonded horizontally aligned graphene sheets bonded by epoxy
linkers.
3. The object of claim 1 wherein the coating consists of
non-functionalized graphene sheets dispersed in low outgassing
epoxy.
4. The object of claim 1 wherein the graphene coated layer has a
gas permeability less than 0.01 ccmil/100 in.sup.2/24 h/atm and
outgassing properties of CVCM of less than 0.1 percent and TML less
than 1 percent.
5. A cured composition of matter comprising horizontally aligned
graphene sheets dispersed in a NASA approved low outgassing
epoxy.
6. The composition of matter of claim 5, wherein the epoxy is a
NASA approved low outgassing epoxy and the cured layer has a gas
permeability of less than 0.01 ccmil/100 in.sup.2/24 h/atm.
7. The coated composition of matter of claim 5 where the gas
comprises of at least one of methane, ethane, higher volatile
hydrocarbons, oxygen, nitrogen, carbon monoxide, hydrogen and
carbon dioxide.
8. The composition of matter of claim 5, wherein the composition of
matter comprises from 0.3 to 10 percent graphene by weight.
9. A method, comprising: depositing graphene into a hardener;
mixing the hardener and the graphene to produce a homogenous
composite mixture; adding a resin material to the composite mixture
to produce an epoxy graphene material; coating a structure with the
epoxy graphene material; aligning the graphene sheets in the
in-plane orientation; and curing the epoxy graphene material.
10. The method of claim 9, further comprising exfoliating the
graphene prior to depositing the graphene into a hardener.
11. The method of claim 9, wherein mixing comprises using a high
shear mixer.
12. The method of claim 9, wherein using a high shear mixer
comprises using an acoustic mixer.
13. The method of claim 9, wherein coating a structure with the
epoxy graphene material comprises using a robotic arm with a
dispensing nozzle.
14. The method of claim 9, wherein coating a structure comprises
coating a structure with a layer of the epoxy graphene material
having a thickness between 10 and 200 micrometers.
15. The method of claim 9, wherein coating a structure comprises
coating a carbon-fiber reinforced polymer tank.
16. A cryo-compressed hydrogen tank, comprising: a carbon-fiber
polymer reinforced body, having an inner surface; and a
horizontally aligned epoxy-graphene sheets coating on the outer
surface.
17. The tank of claim 16, wherein the epoxy-graphene coating has a
thickness in the range of 10-100 micrometers.
18. The tank of claim 16, wherein the epoxy-graphene coating
consists of a two-component epoxy system mixed with graphene.
Description
TECHNICAL FIELD
[0001] This disclosure relates to cryo-compressed hydrogen tanks,
more particularly to thermal insulation for these tanks.
BACKGROUND
[0002] Hydrogen may act as an energy source or carrier for many
applications, including as a fuel for transportation.
Transportation applications, such as for cars, require compact, and
preferably lightweight, hydrogen storage. Hydrogen has good energy
density by weight by typically poor energy density by volume, so
compact storage requires pressurization of the hydrogen.
[0003] Cryo-compression uses cold hydrogen stored in tanks that can
handle up to 350 bars (5000 pounds psi) of internal pressure. As
the hydrogen warms up from heat transferred in from the
environment, the tank has more time before it needs to vent the
hydrogen. In transportation applications, the vehicle has used
enough hydrogen by that time to keep the pressures below the
venting limit.
[0004] Current cryo-compressed hydrogen tanks with vacuum
insulation current satisfy DOE's 2017 targets for energy density.
However, the thermal insulation performance remains satisfactory
for only 3 weeks or so, as the vacuum quality degrades, as
discussed by SM Aceves, et al., in the International Journal of
Hydrogen Energy, vol. 38 (2013), pp. 2480-2489.
[0005] These tanks typically have an architecture with an inner
pressure vessel with a pressure resistance up to 350 bar, made of
aluminum wrapped with carbon-fiber reinforced polymer (CFRP). A
vacuum and numerous sheets of high reflective metalized plastic
provide high performance thermal insulation. Currently no material
exists to replace the high vacuum without an unacceptable decrease
in the volumetric energy density. It has been determined that the
main reason for pressure increase in the vacuum liner is the
outgassing of volatile hydrocarbon-based resins present in the CFRP
epoxies [Reference: S. Aceves et. al. Project # ST003, Hydrogen AMR
(2010)]. Therefore, it appears that the only viable solution to
extend the vacuum lifetime is to mitigate the outgassing of the
epoxy resin from the CFRP tank walls.
[0006] One possible option would be to use low outgassing epoxy
resins, such as those for space applications, for fabrication of a
CFRP tank with reduced outgassing. CFRP typically contains 40%
epoxy resin. Low outgassing resins are generally very viscous and
cost more than the carbon fibers themselves, and are therefore not
suitable for fabricating a cost-effective CFRP tank. A gas barrier
coating may protect the vacuum exposed surface of the CFRP wall and
may represent a viable, low-cost solution. Current gas barrier
approaches have resulted in expensive, ineffective or difficult to
implement gas barriers. For example, a UV-cured polymer coating
actually result in increased outgassing. Conventional gas barrier
polymers such as EVOH (ethylene vinyl alcohol) and oriented PET
(polyethylene terephthalate) require high temperature extrusion,
typically over 250.degree. C., which is incompatible with CFRP
processes. It is difficult to adhere metal foils onto large CFRP
surfaces without defects and vacuum deposition of metallic gas
barriers costs too much for large surfaces.
SUMMARY
[0007] An embodiment consists of a bilayer object consisting of a
carbon fiber reinforced polymer substrate coated with a composition
of matter comprising horizontally aligned exfoliated graphene
sheets dispersed in an epoxy binder.
[0008] Another embodiment consists of a method including depositing
graphene into a hardener, mixing the hardener and the graphene to
produce a homogenous composite mixture, adding a resin material to
the composite mixture to produce an epoxy graphene material,
coating a structure with the epoxy graphene material, aligning the
graphene sheets in the in-plane orientation, and curing the epoxy
graphene material.
[0009] A cured composition of matter comprising horizontally
aligned graphene sheets dispersed in a NASA approved low outgassing
epoxy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a prior art embodiment of a tank wall.
[0011] FIG. 2 shows an embodiment of a tank wall having a
non-volatile gas barrier.
[0012] FIG. 3 shows a comparison of gas diffusion paths.
[0013] FIG. 4 shows chemically linked graphene networks.
[0014] FIG. 5 shows boding of graphene sheets onto the edges of
carbon fibers from the CFRP tank wall.
[0015] FIG. 6 shows a flowchart of an embodiment of a method to
coat an item with a non-volatile gas barrier.
[0016] FIG. 7 shows a six axis deposition system.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] In some embodiments, the inner vessel is made of aluminum
wrapped with carbon-fiber reinforced polymer (CFRP). These tanks
typically satisfy the Department of Energy's 2017 targets for
energy density. Numerous sheets of high reflective metalized
plastic and a vacuum provide high performance thermal insulation.
No currently available material can replace the high vacuum without
an unacceptable decrease in the volumetric energy density. The only
viable solution to extend the vacuum lifetime is to mitigate the
outgassing of the epoxy resin in the CFRP.
[0018] The embodiments here provide protection to the
vacuum-exposed surface of the CI-RP wall via a gas barrier coating
that is inexpensive, effective and easier to implement. One
embodiment uses a formulation that contains chemically bonded
graphene sheets or flakes. The graphene sheets or flakes are
functionalized with reactive groups. In one embodiment the reactive
particles are amino-functionalized graphene sheets that act as
hardener replacement to create cross-linked graphene-polymer
structures by reaction with epoxies materials. Chemical linking of
the epoxies to the non-volatile graphene renders the whole coating
nonvolatile. The approach to realizing this structure has been
disclosed in U.S. co-pending patent application Ser. No.,
14/840,913. In another embodiment the formulation uses graphene
oxide particles that are cured by reaction of the hydroxyl (OH) and
carboxylic acid groups present onto the graphene sheets with epoxy
groups from the epoxy materials.
[0019] Another embodiment uses dispersed non-functionalized
graphene sheets in low outgassing NASA approved two component epoxy
systems. Graphene acts as gas barrier and unlike standard epoxies
used in CFRP fabrication the cured structure is non-volatile. This
composition is fabricated by using a high shear mixing such as
Resodyne.TM. acoustic mixer to provide a homogeneous formulation
consisting first of graphene dispersed into the hardener. This
composition is stable in time. A cured epoxy layer is created by
mixing the composite formulation described above with an
appropriate amount of epoxy material. Curing at room or high
temperature produces hard highly efficient protective gas
barrier.
[0020] FIG. 1 shows a cross-section of one embodiment of a
currently available cryo-compressed tank 10. The stainless steel
shell 12 encases the carbon-fiber reinforced polymer shell 14. The
area 16 between the shell 12 and the CFRP 14 contains hydrocarbon
vapors 18.
[0021] In contrast, FIG. 2 shows a cross-section of a tank in
accordance with the current embodiments. In this example, the tank
20 has a stainless steel shell 22 and a CFRP inner layer 24. A gas
barrier coating 28 has exceptionally low gas permeation rates
enabled by inter-planar stacked graphene sheets. The region 26 has
very little, if any, hydrocarbon vapors. The barrier also has
mechanical reliability under thermal cycling due to outstanding
bonding strength between the coating and the CI-RP walls, which is
achieved by interpenetration and bonding of the graphene sheets
onto graphene edges of the carbon fibers. The gas barrier coating
also has low outgassing due to chemically linked
polymer-to-graphene networks that make the protective coating
non-volatile. The term `non-volatile` as used here means that that
the material or its components do not evaporate at normal
temperature and pressure.
[0022] Similarly, the term low out-gassing as used here means that
the material meets the NASA standard ASTM E595-07. In this
standard, the materials undergo preconditioning at 50 percent
relative humidity and weighed. The materials then go into the test
chamber for 24 hours at a temperature of 125.degree. C. and the
vacuum at a minimum of 5.times.10.sup.-5 torr. During that time,
materials that outgas from the sample escape through a port in the
test chamber and condense on a cooled (25.degree. C.) collector
plate. The material in the chamber and the material that collects
on the collector plate are then weighed to determine the total mass
lost (TML) by the material and the amount of collected volatile
condensable materials (CVCM) on the collector plate. If CVCM<0.1
percent and TML<1 percent, the material passes. Materials that
pass the test are considered to be 'low-outgassing.
[0023] The gas barrier coating contains optimal plate-like
particles The most promising particles are exfoliated graphene
sheets, which have been shown to decrease the permeation rate of
oxygen by 1000.times. when compared to the same polymer without
graphene. The low permeation rate results from the creation of a
tortuous diffusion path for the penetrating gas molecules.
[0024] FIG. 3 contrasts a typical polymer film compared to a
polymer-graphene film. The typical polymer film 30 has a relatively
short pathway 34. The gas molecules 32 stored in the tank travel
the short pathway, increasing the likelihood of the gas molecules
outgassing. The polymer 40 has within it exfoliated, plate-like,
graphene sheets 46. The tortuous path 44 that the gas molecules 42
take make it difficult for them to escape, resulting in a
low-outgassing coating. The permeation rate is expected to be
decreased even more, an additional 10.times., for the hydrocarbons
outgassing from the CFRP. Based upon data published by A. Al.
Jabareen et al., in the Journal of Applied Polymer Science, (2012)
pp. 1534-39, a gas barrier with 1.5% graphene is expected to have
hydrocarbon permeability<0.01 ccmil/100 in.sup.2/24 h/atm. The
inventors have performed calculations that indicate that this
permeability would enable years of vacuum insulation performance
before any servicing is needed.
[0025] Unlike organic molecules, the inorganic graphene particles
are not volatile. While the polymer in which the graphene sheets
are embedded could be volatile, bonding the polymer chains directly
to the graphene sheets can eliminate any volatility, preventing
outgassing from the structure, as described with such as
functionalized, chemically linked graphene sheets 46, such as amino
graphene or graphene oxide, in one embodiment, shown in FIG. 4.
Alternatively, if outgassing epoxy materials are being used then
non-functional horizontally-aligned graphene sheets can be
dispersed and aligned to produce the nonvolatile gas barrier
coating as shown in FIG. 5.
[0026] As can be seen in FIG. 5, the graphene sheets 46 are bonded
on to the edges of carbon fibers from the CRFP tank wall shown in
the highlighted regions 48. This produces a coating that does not
delaminate, as would happen with a protective coating made from a
different material having different chemical and thermal
behaviors.
[0027] A tank with 10 micrometers coating of the proposed
protective gas barrier will only need basic vacuum servicing once
per year. Thicker barrier layers have the potential for further
vacuum lifetime improvements. Even coatings 100 micrometers think
will have a negligible impact on the volumetric and gravimetric
density of the storage tank. This technology can be easily applied
to design tanks for other gases typically stored below room
temperature, such a liquid natural gas. The embodiments here enable
cryo-compressed hydrogen tanks with vacuum insulation lifetimes
20.times. longer than today's state-of-the-art cryogenic tanks.
This enables cryo-compressed hydrogen tanks for automotive
applications with a heat leakage rate below 5 W per 100 liter
storage capacity during 10 years. The thickness of the protective
layer can be anywhere 1 micron to 1 millimeter.
[0028] FIG. 6 shows an embodiment of a process for manufacturing
cured graphene/epoxy coating formulations. In this embodiment, a
two component epoxy is used, one that includes a hardener and a
resin. Initially, graphene is deposited into the hardener component
at 50. The process then mixes the hardener and the graphene at 52.
In one embodiment the graphene is functionalized graphene such as
amino-graphene or graphene oxide sheets. In this case, the amount
of hardener required for curing is decreased accordingly in order
to compensate for the additional curing functional groups (amino,
carboxylic acid or or hydroxyl). In another embodiment
non-functionalized graphene sheets are dispersed in low outgassing
two component epoxy systems, as defined by the NASA standard
mentioned above. In both embodiments graphene acts as a gas barrier
and unlike standard epoxies used in CFRP fabrication the cured
structure is nonvolatile.
[0029] In one embodiment, the process uses high shear mixing, such
as with a Resodyne acoustic mixer or Thinky planetary mixer to
produce a homogenous composite formulation consisting first of
graphene dispersed into the hardener. This composition is stable in
time.
[0030] A cured epoxy layer is created by mixing the composite from
52 with the resin component to produce epoxy graphene material at
54. This mixture is then used to coat a structure such as the inner
surfaces of a cryo-compressed hydrogen tank at 56. In one
embodiment, a 6-axis nozzle dispenser could be used. Once
dispensed, the coating then undergoes curing, either at high
temperature or room temperature. These produce hard, highly
efficient, protective barriers.
[0031] Highly dispersed exfoliated graphene sheets are a necessary
but not a sufficient condition to achieve outstanding gas barrier
performance. Another critical requirement is the creation of
stacked multilayered aligned graphene sheets structures. Shear
based alignment of nanoplatelets has been demonstrated with a
number of polymeric and particle systems [Reference: M. M. Malwitz
et al., Phys. Chem. Chem. Phys. 6.11 (2004): 2977-2982]. This
particular method of alignment has the advantage of being both high
throughput and readily compatible with rotary coating. The tank is
loaded onto a rotary actuator and a custom developed printhead with
a high shear slot die or nozzle will be passed along the profile of
the tank using a robotic arm to create an even coating around the
tank
[0032] FIG. 8 shows an embodiment of a six-axis deposition system
used for coating irregularly shaped surfaces. On the left side, the
system 62 is shown coating a tank 62. On the right side, the nozzle
62 is applying the aligned graphene sheets 46 onto the tank 60. An
example of such a system is disclosed in US Patent Publication
20160176111.
[0033] In this manner, a relatively impermeable gas barrier can be
formed on many different types of structures. The process is
inexpensive, efficient and easy to manufacture compared to current
gas barrier coatings.
[0034] It will be appreciated that variants of the above-disclosed
and other features and functions, or alternatives thereof, may be
combined into many other different systems or applications. Various
presently unforeseen or unanticipated alternatives, modifications,
variations, or improvements therein may be subsequently made by
those skilled in the art which are also intended to be encompassed
by the following claims.
* * * * *